In JS a Boolean has 4 states.
true
false
undefined (where the key is set to undefined)
undefined (where the key doesn’t exist on the object)
if (obj.value === true) {
console.log(1);
} elseif (obj.value === false) {
console.log(2);
} elseif ("value" in obj) { // key "value" is in the obj, but it is set to undefined console.log(3);
} else { // key "value" is not in objectconsole.log(4);
}
This is JavaScript undefined logic specifically where it means the key isn’t present on the object.
Except you can add the key with an undefined value and it may have different behaviors than if the key was really not there.
Please add a trigger warning to this in the future, this is too scary
In JS a Boolean has 4 states.
true
false
undefined (where the key is set to undefined)
undefined (where the key doesn’t exist on the object)
if (obj.value === true) { console.log(1); } else if (obj.value === false) { console.log(2); } else if ("value" in obj) { // key "value" is in the obj, but it is set to undefined console.log(3); } else { // key "value" is not in object console.log(4); }You’re welcome.
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